1. Field of the Invention
This invention relates generally to Physical Vapor Deposition (xe2x80x9cPVDxe2x80x9d) systems, and more particularly to an apparatus and method for improving PVD processes using an open top Hollow Cathode Magnetron (xe2x80x9cHCMxe2x80x9d) source.
2. Description of the Background Art
Physical vapor deposition (xe2x80x9cPVDxe2x80x9d) is a well known technique for depositing metal layers onto semiconductor wafers (also referred to herein as xe2x80x9csubstratesxe2x80x9d). These thin metal layers can be used as diffusion barriers, adhesion or seed layers, primary conductors, antireflection coatings, and etch stops, etc.
In a conventional Hollow Cathode Magnetron (xe2x80x9cHCMxe2x80x9d), magnetic fields are used to generate a high density plasma of Argon (xe2x80x9cArxe2x80x9d) or other suitable inert gas and target material within a cathode of the HCM. The magnetic fields are also used to confine the plasma within the HCM. The cathode has a target, which can be made of metals such as Tantalum (xe2x80x9cTaxe2x80x9d), Aluminum (xe2x80x9cAlxe2x80x9d), Titanium (xe2x80x9cTixe2x80x9d), Copper (xe2x80x9cCuxe2x80x9d), or other suitable metal. A power supply supplies a negative potential to the target such that the magnetic fields in combination with the negative potential cause plasma ions to hit the target with high energy, which in turn cause target atoms to dislodge from the surface of the target by direct momentum transfer and also create secondary electrons. These dislodged atoms and ions (created by the secondary electrons) are then deposited on the semiconductor wafer.
However, the atoms are typically dislodged from the sidewall of the target at a higher rate than at the top of the target. This can lead to more deposition than erosion at the top of the target. Redeposition has a higher potential to form particles or delamination than an eroded area of the target.
The present invention provides a system for performing PVD using an open top HCM source, increasing the efficiency of using target material and decreasing redeposition. In one embodiment, the apparatus comprises a HCM with an open top cylindrical sputtering target having a negative bias, thereby forming an electric filed within the HCM to generate a plasma. To seal the HCM for PVD processes, a shield is placed on the top of HCM in place of target material, thereby allowing the HCM to be evacuated. The HCM also comprises electromagnetic coils that shape and increase density of a plasma of inert gas within the HCM. Plasma ions strike the target, thereby dislodging target atoms, which then deposit on the wafer.
In another embodiment of the invention, the HCM uses a flat annular target arranged in a horizontal position in place of the cylindrical target. In a third embodiment of the invention, the HCM uses a conical open top target arranged at a 45-degree angle. It will be recognized by one skilled in the art that in alternative embodiments the open top target can be shaped and aligned at any angle.
As the target in each of the above-mentioned embodiments does not have a top/central portion, the HCM is more efficient to operate since the target comprises less metal but does not lower deposition rates. Further, using the conical open top target leads to more target material flowing out of a mouth of the target than in a conventional HCM because the target mouth has many times the area of the open top of the target, thereby yielding higher deposition rates. In addition, redeposition becomes less of a problem since the target does not contain a top portion on which redeposited particles can form.
The present invention further provides a method for PVD using a topless target. The method uses the apparatus described above and comprises the steps of maintaining a plasma within a cathode of the HCM; sputtering target material from the open top target; and depositing the sputtered target material onto the wafer.
The system and method may advantageously perform PVD onto a wafer using an open top target while improving on the deposition rate of a conventional HCM.